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The two PN-12s represented the definitive design. Like its predecessors in the PN-series, the PN-12 was a biplane designed specifically for the patrol/antisubmarine role. Single .30-caliber machine guns were fitted in the bow and amidships, and four 230-pound bombs could be carried under the lower wing. Equally powered by twin 525-hp engines, one PN-12 had twin Pratt and Whitney Hornet R-1850s, and the other Wright Cyclone R-1750s. They gave the aircraft a top speed of 114 mph and a range at cruising speed of just over 1,300 miles. It was flown by a crew of five (in open cockpits), and a relief crew could be carried for long patrols. On 3-5 May 1928, the Cyclone-powered PN-12 set another world seaplane record, covering a distance of 1,243 statue miles in 17 hours, 55 minutes.

The Naval Aircraft Factory was not capable of large-scale production, and the Navy decided to have the PN-12 manufactured by private aircraft companies. The Douglas Aircraft Company produced 25 PD-1 aircraft and the Martin Company built 30 PM-1 variants based on the NAF design. Subsequently, Martin built 25 PM-2 variants and the Keystone Aircraft Corporation built 18 similar PK-1 aircraft, the latter being twin-rudder versions. Thus, the PN-12 gave birth to 98 offspring. These aircraft served in the Fleet until 1938.

In 1927 the Hall Aluminum Aircraft Company developed another PN derivative, the XPH-1. 2 This was the first U.S. Navy flying boat to have all-metal stressed skin construction, which provided a considerable savings in weight. In the event, only ten PH-1s were built as the Navy moved to more advanced flying boat designs. But the Coast Guard procured seven improved Hall PH-2s and seven PH-3s for air-sea rescue missions. Some of these aircraft served into World War II.

Thus, the same basic flying boat design-from the F-5-L to the PH-3-spanned two world wars, a most notable achievement.